TTI Bundling for Downlink Communication

ABSTRACT

This disclosure relates to TTI bundling for downlink communication. According to one embodiment, a base station and a wireless device may establish a wireless communication link. The base station may determine to enable TTI bundling for downlink communication for at least one carrier of the wireless communication link. The base station may provide an indication to the wireless device to enable TTI bundling for downlink communication for the determined carrier(s) of the wireless communication link. The base station may subsequently transmit TTI bundle downlink communications to the wireless device via the determined carrier(s).

PRIORITY CLAIM

The present is a continuation of U.S. patent application Ser. No.14/496,385, filed Sep. 25, 2014, which claims benefit of priority toU.S. Provisional Application No. 61/920,263 titled “TTI Bundling forDownlink Communication” and filed on Dec. 23, 2013, and to U.S.Provisional Application No. 61/927,566 titled “TTI Bundling for DownlinkCommunication” and filed on Jan. 15, 2014, which are hereby incorporatedby reference in their entirety as though fully and completely set forthherein.

FIELD

The present application relates to wireless devices, and moreparticularly to a system and method for performing transmission timeinterval (TTI) bundling in the downlink of a wireless communicationsystem.

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage.Additionally, there exist numerous different wireless communicationtechnologies and standards. Some examples of wireless communicationstandards include GSM, UMTS (associated with, for example, WCDMA orTD-SCDMA air interfaces), LTE, LTE Advanced (LTE-A), HSPA, 3GPP2CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), IEEE 802.11 (WLAN orWi-Fi), IEEE 802.16 (WiMAX), Bluetooth, and others.

In some wireless communication systems, such as certain cellularcommunication networks, wireless communication is performed on frequencybands which have been licensed (e.g., by a cellular network provider).Additionally, in some wireless communication systems, such as Wi-Fi andBluetooth wireless communication systems, wireless communication isperformed on unlicensed frequency bands, such as the 2.4 GHz ISMfrequency band.

SUMMARY

Embodiments are presented herein of, inter alfa, methods for performingtransmission time interval (TTI) bundling in the downlink of a wirelesscommunication system, and of devices configured to implement themethods.

According to the techniques described herein, a base station and awireless device may establish a wireless communication link according toa wireless communication technology. At least in some instances, thewireless communication link may include carrier aggregation, such thatat least a primary component carrier and a secondary component carrierare established between the base station and the wireless device.

The base station may determine to enable TTI bundling for downlinkcommunications between the base station and the wireless device. TTIbundling may be enabled for any of a variety of reasons, in order toprovide more robust downlink communication characteristics. For example,if downlink transmit power on a component carrier is limited (e.g., dueto regulations on a frequency band on which the component carrier isdeployed), TTI bundling may be enabled in order to compensate for thelimited transmit power available. As another possibility, if acommunication channel is experiencing degraded channel conditions,and/or experiences substantial signal attenuation as a qualitativecharacteristic of the communication channel, TTI bundling may be enabledto compensate for such considerations. Other reasons (includingcombinations of the above reasons and/or additional reasons) may alsoprovide the basis for a base station to determine to enable TTIbundling.

After determining to do so, the base station may provide an indicationto the wireless device to enable TTI bundling. The base station and thewireless device may then subsequently engage in downlink communicationusing TTI bundling.

If desired, such downlink TTI bundling may be enabled on a per-carrierbasis. This may allow the base station and the wireless device toperform downlink communication with TTI bundling on component carriersfor which conditions warrant it (for example, on a secondary componentcarrier in an unlicensed frequency band, which may be subject totransmit power limits, interference due to other wireless communicationtechnologies, etc.) while performing downlink communication without TTIbundling on component carriers for which conditions are sufficientlygood as to render it unnecessary (for example, on a primary componentcarrier in a licensed frequency band).

Note that the techniques described herein may be implemented in and/orused with a number of different types of devices, including but notlimited to, base stations, access points, cellular phones, portablemedia players, tablet computers, wearable devices, and various othercomputing devices.

This Summary is intended to provide a brief overview of some of thesubject matter described in this document. Accordingly, it will beappreciated that the above-described features are merely examples andshould not be construed to narrow the scope or spirit of the subjectmatter described herein in any way. Other features, aspects, andadvantages of the subject matter described herein will become apparentfrom the following Detailed Description, Figures, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present subject matter can be obtainedwhen the following detailed description of the embodiments is consideredin conjunction with the following drawings, in which:

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem, according to one embodiment;

FIG. 2 illustrates a base station (BS), or “eNB” in LTE, incommunication with a user equipment (UE) device, according to oneembodiment;

FIG. 3 illustrates an exemplary block diagram of a UE, according to oneembodiment;

FIG. 4 illustrates an exemplary block diagram of a BS, according to oneembodiment;

FIG. 5 illustrates an exemplary carrier aggregation scheme, according toone embodiment;

FIG. 6 is a communication flow diagram illustrating an exemplary methodfor performing TTI bundling in the downlink of a wireless communicationsystem, according to one embodiment; and

FIG. 7 illustrates an exemplary communication scheme in which TTIbundling is used for downlink communication, according to oneembodiment.

While the features described herein may be susceptible to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and are herein described indetail. It should be understood, however, that the drawings and detaileddescription thereto are not intended to be limiting to the particularform disclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the subject matter as defined by the appended claims.

DETAILED DESCRIPTION Terms

The following is a glossary of terms used in this disclosure:

Memory Medium—Any of various types of non-transitory memory devices orstorage devices. The term “memory medium” is intended to include aninstallation medium, e.g., a CD-ROM, floppy disks, or tape device; acomputer system memory or random access memory such as DRAM, DDR RAM,SRAM, EDO RAM, Rambus RAM, etc.; a non-volatile memory such as a Flash,magnetic media, e.g., a hard drive, or optical storage; registers, orother similar types of memory elements, etc. The memory medium mayinclude other types of non-transitory memory as well or combinationsthereof. In addition, the memory medium may be located in a firstcomputer system in which the programs are executed, or may be located ina second different computer system which connects to the first computersystem over a network, such as the Internet. In the latter instance, thesecond computer system may provide program instructions to the firstcomputer for execution. The term “memory medium” may include two or morememory mediums which may reside in different locations, e.g., indifferent computer systems that are connected over a network. The memorymedium may store program instructions (e.g., embodied as computerprograms) that may be executed by one or more processors.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Programmable Hardware Element—includes various hardware devicescomprising multiple programmable function blocks connected via aprogrammable interconnect. Examples include FPGAs (Field ProgrammableGate Arrays), PLDs (Programmable Logic Devices), FPOAs (FieldProgrammable Object Arrays), and CPLDs (Complex PLDs). The programmablefunction blocks may range from fine grained (combinatorial logic or lookup tables) to coarse grained (arithmetic logic units or processorcores). A programmable hardware element may also be referred to as“reconfigurable logic”.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), television system, grid computing system, or otherdevice or combinations of devices. In general, the term “computersystem” can be broadly defined to encompass any device (or combinationof devices) having at least one processor that executes instructionsfrom a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems devices which are mobile or portable and which performs wirelesscommunications. Examples of UE devices include mobile telephones orsmart phones (e.g., iPhone™, Android™-based phones), portable gamingdevices (e.g., Nintendo DS™, Play Station Portable™, Gameboy Advance™,iPhone™), laptops, wearable devices (e.g., smart watch, smart glasses),PDAs, portable Internet devices, music players, data storage devices, orother handheld devices, etc. In general, the term “UE” or “UE device”can be broadly defined to encompass any electronic, computing, and/ortelecommunications device (or combination of devices) which is easilytransported by a user and capable of wireless communication.

Base Station—The term “Base Station” has the full breadth of itsordinary meaning, and at least includes a wireless communication stationinstalled at a fixed location and used to communicate as part of awireless telephone system or radio system.

Processing Element—refers to various elements or combinations ofelements. Processing elements include, for example, circuits such as anASIC (Application Specific Integrated Circuit), portions or circuits ofindividual processor cores, entire processor cores, individualprocessors, programmable hardware devices such as a field programmablegate array (FPGA), and/or larger portions of systems that includemultiple processors.

Channel—a medium used to convey information from a sender (transmitter)to a receiver. It should be noted that since characteristics of the term“channel” may differ according to different wireless protocols, the term“channel” as used herein may be considered as being used in a mannerthat is consistent with the standard of the type of device withreference to which the term is used. In some standards, channel widthsmay be variable (e.g., depending on device capability, band conditions,etc.). For example, LTE may support scalable channel bandwidths from 1.4MHz to 20 MHz. In contrast, WLAN channels may be 22 MHz wide whileBluetooth channels may be 1 Mhz wide. Other protocols and standards mayinclude different definitions of channels. Furthermore, some standardsmay define and use multiple types of channels, e.g., different channelsfor uplink or downlink and/or different channels for different uses suchas data, control information, etc.

Band—The term “band” has the full breadth of its ordinary meaning, andat least includes a section of spectrum (e.g., radio frequency spectrum)in which channels are used or set aside for the same purpose.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually”, where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

FIGS. 1 and 2—Communication System

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem, according to one embodiment. It is noted that the system of FIG.1 is merely one example of a possible system, and embodiments may beimplemented in any of various systems, as desired.

As shown, the exemplary wireless communication system includes a basestation 102A which communicates over a transmission medium with one ormore user devices 106A, 106B, etc., through 106N. Each of the userdevices may be referred to herein as a “user equipment” (UE). Thus, theuser devices 106 are referred to as UEs or UE devices.

The base station 102A may be a base transceiver station (BTS) or cellsite, and may include hardware that enables wireless communication withthe UEs 106A through 106N. The base station 102A may also be equipped tocommunicate with a network 100 (e.g., a core network of a cellularservice provider, a telecommunication network such as a public switchedtelephone network (PSTN), and/or the Internet, among variouspossibilities). Thus, the base station 102A may facilitate communicationbetween the user devices and/or between the user devices and the network100.

The communication area (or coverage area) of the base station may bereferred to as a “cell.” The base station 102A and the UEs 106 may beconfigured to communicate over the transmission medium using any ofvarious radio access technologies (RATs), also referred to as wirelesscommunication technologies, or telecommunication standards, such as GSM,UMTS (WCDMA, TD-SCDMA), LTE, LTE-Advanced (LTE-A), HSPA 3GPP2 CDMA2000(e.g., 1xRTT, NEV-DO, HRPD, eHRPD), Wi-Fi, WiMAX etc.

Base station 102A and other similar base stations (such as base stations102B . . . 102N) operating according to the same or a different cellularcommunication standard may thus be provided as a network of cells, whichmay provide continuous or nearly continuous overlapping service to UEs106A-N and similar devices over a wide geographic area via one or morecellular communication standards.

Thus, while base station 102A may act as a “serving cell” for UEs 106A-Nas illustrated in FIG. 1, each UE 106 may also be capable of receivingsignals from (and possibly within communication range of) one or moreother cells (which might be provided by base stations 102B-N and/or anyother base stations), which may be referred to as “neighboring cells”.Such cells may also be capable of facilitating communication betweenuser devices and/or between user devices and the network 100, accordingto the same wireless communication technology as base station 102Aand/or any of various other possible wireless communicationtechnologies. Such cells may include “macro” cells, “micro” cells,“pico” cells, and/or cells which provide any of various othergranularities of service area size. For example, base stations 102A-Billustrated in FIG. 1 might be macro cells, while base station 102Nmight be a micro cell. Other configurations are also possible.

Note that a UE 106 may be capable of communicating using multiplewireless communication standards. For example, a UE 106 may beconfigured to communicate using a wireless networking (e.g., Wi-Fi)and/or peer-to-peer wireless communication protocol (e.g., BT, Wi-Fipeer-to-peer, etc.) in addition to at least one cellular communicationprotocol (e.g., GSM, UMTS (WCDMA, TD-SCDMA), LTE, LTE-A, HSPA, 3GPP2CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), etc.). The UE 106 may alsoor alternatively be configured to communicate using one or more globalnavigational satellite systems (GNSS, e.g., GPS or GLONASS), one or moremobile television broadcasting standards (e.g., ATSC-M/H or DVB-H),and/or any other wireless communication protocol, if desired. Othercombinations of wireless communication standards (including more thantwo wireless communication standards) are also possible.

FIG. 2 illustrates user equipment 106 (e.g., one of the devices 106Athrough 106N) in communication with a base station 102 (e.g., one of thebase stations 102A through 102N), according to one embodiment. The UE106 may be a device with cellular communication capability such as amobile phone, a hand-held device, a wearable device, a computer or atablet, or virtually any type of wireless device.

The UE 106 may include a processor that is configured to execute programinstructions stored in memory. The UE 106 may perform any of the methodembodiments described herein by executing such stored instructions.Alternatively, or in addition, the UE 106 may include a programmablehardware element such as an FPGA (field-programmable gate array) that isconfigured to perform any of the method embodiments described herein, orany portion of any of the method embodiments described herein.

The UE 106 may include one or more antennas for communicating using oneor more wireless communication protocols or technologies. In oneembodiment, the UE 106 might be configured to communicate using eitherof CDMA 2000 (1xRTT/1xEV-DO/HRPD/eHRPD) or LTE using a single sharedradio and/or GSM or LTE using the single shared radio. The shared radiomay couple to a single antenna, or may couple to multiple antennas(e.g., for MIMO) for performing wireless communications. In general, aradio may include any combination of a baseband processor, analog RFsignal processing circuitry (e.g., including filters, mixers,oscillators, amplifiers, etc.), or digital processing circuitry (e.g.,for digital modulation as well as other digital processing). Similarly,the radio may implement one or more receive and transmit chains usingthe aforementioned hardware. For example, the UE 106 may share one ormore parts of a receive and/or transmit chain between multiple wirelesscommunication technologies, such as those discussed above.

In some embodiments, the UE 106 may include separate (and possiblymultiple) transmit and/or receive chains (e.g., including separate RFand/or digital radio components) for each wireless communicationprotocol with which it is configured to communicate. As a furtherpossibility, the UE 106 may include one or more radios which are sharedbetween multiple wireless communication protocols, and one or moreradios which are used exclusively by a single wireless communicationprotocol. For example, the UE 106 might include a shared radio forcommunicating using either of LTE or 1xRTT (or LTE or GSM), and separateradios for communicating using each of Wi-Fi and Bluetooth. Otherconfigurations are also possible.

FIG. 3—Exemplary Block Diagram of a UE

FIG. 3 illustrates an exemplary block diagram of a UE 106, according toone embodiment. As shown, the UE 106 may include a system on chip (SOC)300, which may include portions for various purposes. For example, asshown, the SOC 300 may include processor(s) 302 which may executeprogram instructions for the UE 106 and display circuitry 304 which mayperform graphics processing and provide display signals to the display360. The processor(s) 302 may also be coupled to memory management unit(MMU) 340, which may be configured to receive addresses from theprocessor(s) 302 and translate those addresses to locations in memory(e.g., memory 306, read only memory (ROM) 350, NAND flash memory 310)and/or to other circuits or devices, such as the display circuitry 304,wireless communication circuitry 330, connector I/F 320, and/or display360. The MMU 340 may be configured to perform memory protection and pagetable translation or set up. In some embodiments, the MMU 340 may beincluded as a portion of the processor(s) 302.

As shown, the SOC 300 may be coupled to various other circuits of the UE106. For example, the UE 106 may include various types of memory (e.g.,including NAND flash 310), a connector interface 320 (e.g., for couplingto a computer system, dock, charging station, etc.), the display 360,and wireless communication circuitry (e.g., radio) 330 (e.g., for LTE,Wi-Fi, GPS, etc.).

The UE device 106 may include at least one antenna, (and possiblymultiple antennas, e.g., for MIMO and/or for implementing differentwireless communication technologies, among various possibilities)performing wireless communication with base stations and/or otherdevices. For example, the UE device 106 may use antenna(s) 335 toperform the wireless communication. As noted above, the UE 106 may beconfigured to communicate wirelessly using multiple wirelesscommunication technologies in some embodiments.

As described further subsequently herein, the UE 106 may includehardware and software components for implementing features for TTIbundling for downlink communication, such as those described herein withreference to, inter alfa, FIG. 6. The processor 302 of the UE device 106may be configured to implement part or all of the methods describedherein, e.g., by executing program instructions stored on a memorymedium (e.g., a non-transitory computer-readable memory medium). Inother embodiments, processor 302 may be configured as a programmablehardware element, such as an FPGA (Field Programmable Gate Array), or asan ASIC (Application Specific Integrated Circuit). Alternatively (or inaddition) the processor 302 of the UE device 106, in conjunction withone or more of the other components 300, 304, 306, 310, 320, 330, 335,340, 350, 360 may be configured to implement part or all of the featuresdescribed herein, such as the features described herein with referenceto, inter alfa, FIG. 6.

FIG. 4—Exemplary Block Diagram of a Base Station

FIG. 4 illustrates an exemplary block diagram of a base station 102,according to one embodiment. It is noted that the base station of FIG. 4is merely one example of a possible base station. As shown, the basestation 102 may include processor(s) 404 which may execute programinstructions for the base station 102. The processor(s) 404 may also becoupled to memory management unit (MMU) 440, which may be configured toreceive addresses from the processor(s) 404 and translate thoseaddresses to locations in memory (e.g., memory 460 and read only memory(ROM) 450) or to other circuits or devices.

The base station 102 may include at least one network port 470. Thenetwork port 470 may be configured to couple to a telephone network andprovide a plurality of devices, such as UE devices 106, access to thetelephone network as described above in FIGS. 1 and 2.

The network port 470 (or an additional network port) may also oralternatively be configured to couple to a cellular network, e.g., acore network of a cellular service provider. The core network mayprovide mobility related services and/or other services to a pluralityof devices, such as UE devices 106. In some cases, the network port 470may couple to a telephone network via the core network, and/or the corenetwork may provide a telephone network (e.g., among other UE devicesserviced by the cellular service provider).

The base station 102 may include at least one antenna 434, and possiblymultiple antennas. The antenna(s) 434 may be configured to operate as awireless transceiver and may be further configured to communicate withUE devices 106 via radio 430. The antenna 434 communicates with theradio 430 via communication chain 432. Communication chain 432 may be areceive chain, a transmit chain or both. The radio 430 may be configuredto communicate via various wireless telecommunication standards,including, but not limited to, LTE, LTE-A, UMTS, CDMA 2000, Wi-Fi, etc.

The BS 102 may be configured to communicate wirelessly using multiplewireless communication standards. In some instances, the base station102 may include multiple radios, which may enable the base station 102to communicate according to multiple wireless communicationtechnologies. For example, as one possibility, the base station 102 mayinclude an LTE radio for performing communication according to LTE aswell as a Wi-Fi radio for performing communication according to Wi-Fi.In such a case, the base station 102 may be capable of operating as bothan LTE base station and a Wi-Fi access point. As another possibility,the base station 102 may include a multi-mode radio which is capable ofperforming communications according to any of multiple wirelesscommunication technologies (e.g., LTE and Wi-Fi).

As described further subsequently herein, the BS 102 may includehardware and software components for implementing features for TTIbundling for downlink communication, such as those described herein withreference to, inter alia, FIG. 6. The processor 404 of the base station102 may be configured to implement part or all of the methods describedherein, e.g., by executing program instructions stored on a memorymedium (e.g., a non-transitory computer-readable memory medium).Alternatively, the processor 404 may be configured as a programmablehardware element, such as an FPGA (Field Programmable Gate Array), or asan ASIC (Application Specific Integrated Circuit), or a combinationthereof Alternatively (or in addition) the processor 404 of the BS 102,in conjunction with one or more of the other components 430, 432, 434,440, 450, 460, 470 may be configured to implement part or all of thefeatures described herein, such as the features described herein withreference to, inter alfa, FIG. 6.

FIG. 5—Carrier Aggregation

Carrier aggregation is a scheme in which multiple carriers (e.g.,frequency channels) may be used for wireless communication with a UEaccording to a wireless communication technology. FIG. 5 illustrates oneexemplary carrier aggregation scheme (e.g., which may be used inaccordance with the LTE radio access technology) which may be used inaccordance with other aspects of this disclosure, such as with respectto the method of FIG. 6.

In the illustrated scheme, up to five component carriers (carriers 504,506, 508, 510, 512 ) may be aggregated for a single user device (such asone of the UEs 106 illustrated in and described with respect to FIGS.1-3). Each component carrier may use a channel width of up to 20 MHz. Asone possibility, each component carrier may be an LTE release 10 singlecarrier. Thus, according to the exemplary scheme, a UE may be allocatedup to 100 MHz of bandwidth. In many instances, such a carrieraggregation scheme may enable a UE participating in it with greaterthroughput than without such a scheme.

In many cases, component carriers may utilize adjacent frequencychannels. However, it should be noted that it is also possible toimplement carrier aggregation utilizing non-continuous frequencychannels, potentially including non-continuous frequency channels withinthe same frequency band, and/or frequency channels within differentfrequency bands. For example, it may be possible to implement carrieraggregation using a frequency channel in a licensed frequency band asone component carrier, and a frequency channel in an unlicensedfrequency band as another component carrier.

It should be noted that while the exemplary scheme illustrated in FIG. 5and the associated description are provided by way of example as onepossible manner of implementing carrier aggregation, they are notintended to be limiting to the disclosure as a whole. Numerousalternatives to and variations of the details thereof are possible andshould be considered within the scope of the present disclosure. Forexample: carrier aggregation schemes may be implemented in conjunctionwith other wireless communication technologies; carriers according toother LTE releases or other radio access technologies altogether may beused; carriers having different channel widths may be used; differentnumbers of component carriers may be supported; and/or any of numerousother alternatives to and variations of the illustrated scheme are alsopossible.

Note that for systems which implement carrier aggregation, variouscontrol schemes/mechanisms are possible. As one possibility, anindependent cell may be implemented on each component carrier, forexample by providing a control channel with data scheduling and othercontrol features for each cell on the component carrier for that cell.As another possibility, some or all control functions may becentralized. For example, a “primary cell” might be implemented on one(“primary”) component carrier, while “secondary cells” might beimplemented on any additional (“secondary”) component carriers, suchthat some or all control information for the secondary cells iscommunicated by way of the primary cell.

Such a scheme may be referred to as “cross-carrier scheduling”. In sucha scheme, a network may provide control data (e.g., for scheduling userdata communications, performing mobility related functions, etc.) forall cells by way of a control channel of the primary cell. For example,the control data may be communicated by way of a physical downlinkcontrol channel (PDCCH) of the primary cell.

The network may provide user data (e.g., application data for networkingapplications such as web browser applications, email applications voicecall applications, video chat applications, game applications, etc.) toa UE in such a scheme on any or all of the primary or secondary cells.For example, various portions of the user data may be communicated byway of a physical downlink shared channel (PDSCH) of each of the primarycell and the secondary cells.

Thus, cross-carrier scheduling may be used in conjunction with carrieraggregation to centralize (at least a portion of) control communicationson one cell. This technique may be used in many instances forinfrastructure mode communications between a UE and a network. Such atechnique may be particularly useful if different component carriers areknown and/or expected to have different interference levels, since insuch a case the carrier having the lowest interference level mayadvantageously be used for high priority control data. Such a situationmay be the case, for example, if one component carrier is on a licensedfrequency band for which the potential for interference is substantiallylimited to that caused by network controlled wireless communication,while another component carrier is on an unlicensed frequency band whichmay be subject to interference caused by wireless communication which isnot under network control.

FIG. 6—Communication Flow Diagram

FIG. 6 is a communication/signal flow diagram illustrating a scheme fortransmission time interval (TTI) bundling for downlink communication.The scheme shown in FIG. 6 may be used in conjunction with any of thecomputer systems or devices shown in the above Figures, among otherdevices. As shown, according to the scheme a BS 102 (e.g., such asillustrated in and described with respect to FIGS. 1-2 and 4) mayprovide a UE 106 (e.g., such as illustrated in and described withrespect to FIGS. 1-3) with a wireless communication link in which TTIbundling may be enabled and used for DL communication if desired.

TTI bundling may be a modification of a Hybrid Automatic Repeat Request(HARM) feature which may be implemented at the media access control(MAC) layer of a device according to some wireless communicationtechnologies. Typically the use of HARQ may include waiting for anACK/NACK after a first transmission attempt, and if it is determinedthat the first transmission attempt was unsuccessful, performing a HARQretransmission. This may be repeated up to a certain (e.g., networkconfigured maximum) number of retransmissions. In the case of TTIbundling, instead of waiting for an ACK/NACK before performing a HARQretransmission, multiple HARQ transmissions of a single packet may beperformed in successive TTIs. This feature may provide very robustpacketized transmissions with low latency, which may be useful fortraffic types with strict latency and/or reliability requirements (suchas voice communications) in difficult RF conditions.

In various embodiments, some of the elements of the scheme shown may beperformed concurrently, in a different order than shown, or may beomitted. Additional elements may also be performed as desired. As shown,the scheme may operate as follows.

In 602, a wireless communication link may be established between the UE106 and the BS 102. The wireless communication link may be establishedaccording to a first wireless communication technology (or “radio accesstechnology” or “RAT”), such as LTE.

Establishing the wireless communication link may include establishing(e.g., configuring) a primary component carrier (or “primary carrier” or“primary cell”) between the BS 102 and the UE 106. The primary carriermay be established on a particular (“first”) channel (e.g., a frequencychannel).

In some cases, establishing the wireless communication link may alsoinclude establishing (e.g., configuring) a secondary component carrier(or “secondary carrier” or “secondary cell”) between the BS 102 and theUE 106. The secondary carrier may be established on a different(“second”) channel (e.g., a frequency channel) than the first channel.In other words, the wireless communication link may support / implementcarrier aggregation, in some instances.

The first channel may be a channel in a licensed frequency band, whichmay also be referred to herein as a “first frequency band”. For example,a cellular network provider may have licensed a particular frequencyband (possibly specifically for use in conjunction with a particularradio access technology, such as LTE-A, LTE, WCDMA, CDMA2000, GSM,etc.), and may provide radio access to its cellular network via thatlicensed frequency band. Such a licensed frequency band may be subjectto less external interference than an unlicensed frequency band. Forexample, an unlicensed frequency band might be subject to interferencefrom other wireless communication technologies and/or from othercellular network operators utilizing a similar or the same wirelesscommunication technology in the unlicensed frequency band, whereas alicensed frequency band may not be subject to such external interferencesources, e.g., if the licensed frequency band is licensed for theexclusive use of one particular cellular network provider. The secondchannel may also be a channel in a licensed frequency band (e.g., thefirst frequency band or another licensed frequency band) or may be achannel in an unlicensed frequency band.

The wireless communication link may provide the UE 106 with acommunication link to a cellular network, such as a core network of acellular service provider (e.g., with which a user of the UE 106 mayhave a subscription and/or other agreement to provide cellular service).The cellular network may thus provide connectivity between the userdevice and various services and/or devices coupled to the cellularnetwork, such as other user devices, a public switched telephonenetwork, the Internet, various cloud-based services, etc.

In 604, the BS 102 may provide an indication to the UE 106 to enable TTIbundling for downlink communications between the BS 102 and the UE 106.The indication may be provided in any of a variety of ways. As onepossibility, the indication may take the form of a (e.g., Boolean,bitmap, etc.) parameter (e.g., a “ttiBundling_DL” parameter) which maybe included in an information element (IE) in a radio resource control(RRC) message. In such an instance, the IE may be a MAC-MainConfig IE,which is an IE that can be used to specify the MAC main configurationfor signaling and data radio bearers.

Note that if the wireless communication link provides carrieraggregation, it may be the case that the indication to enable TTIbundling for downlink communications between the BS and the UE furtherspecifies to enable TTI bundling for downlink communications between theBS and the UE on a specific carrier (e.g. the primary carrier, or thesecondary carrier). In other words, downlink TTI bundling may be enabledon a per-carrier basis, if desired. Alternatively, the indication toenable TTI bundling for downlink communications between the BS and theUE may apply to all component carriers, if desired.

As previously noted, unlicensed frequency bands may be subject tocertain conditions which may negatively affect channel conditions,including but not limited to interference from other types of wirelesscommunication such as Wi-Fi. It should be further noted that unlicensedfrequency bands may also be subject to maximum transmission powerlimitations (e.g., imposed by regulatory bodies such as the UnitedStates Federal Communication Commission (FCC)). Furthermore, at least insome instances, downlink communications on unlicensed frequency bandsmay be performed on higher-frequency communication channels (e.g., 5.8GHz, vs. 2 GHz in the uplink) which may be subject to significant signalattenuation.

Thus, as one possibility, the indication to enable TTI bundling mayspecify to enable TTI bundling for downlink communications between theBS 102 and the UE 106 on the secondary carrier, which may utilize achannel on an unlicensed frequency band.

Alternatively or additionally, in an instance where a ttiBundling_DL IEis used to configured downlink TTI bundling, a correspondingttiBundling_UL IE may be used to configure uplink TTI bundling. ThettiBundling_UL IE may include information such as that indicated by thettiBundling field as defined in 3GPP Technical Specification (TS) 36.331version 11.5.0 (which is incorporated by reference for all purposes asif fully set forth herein), modified as necessary to reflect that thefield relates specifically to configuring TTI bundling for the uplink.

Alternatively or additionally, in an instance where a ttiBundling_DL IEis included in a MAC-MainConfig IE, the MAC-MainConfig IE may includefields such as the following:

MAC-MainConfig field descriptions dl-PathlossChange DL Pathloss Changeand the change of the required power backoff due to power management (asallowed by P-MPRc [42]) for PHR reporting in TS 36.321 [6]. Value in dB.Value dB1 corresponds to 1 dB, dB3 corresponds to 3 dB and so on. Thesame value applies for each serving cell (although the associatedfunctionality is performed independently for each cell). drx-Config Usedto configure DRX as specified in TS 36.321 [6]. E-UTRAN configures thevalues in DRX-Config-v1130 only if the UE indicates support for IDCindication. E-UTRAN configures drx-Config-v1130 only if drx-Config(without suffix) is configured. drx-InactivityTimer Timer for DRX in TS36.321 [6]. Value in number of PDCCH sub-frames. Value psf1 correspondsto 1 PDCCH sub-frame, psf2 corresponds to 2 PDCCH sub-frames and so on.drx-RetransmissionTimer Timer for DRX in TS 36.321 [6]. Value in numberof PDCCH sub-frames. Value psf1 corresponds to 1 PDCCH sub-frame, psf2corresponds to 2 PDCCH sub-frames and so on. In casedrx-RetransmissionTimer-v1130 is signalled, the UE shall ignoredrx-RetransmissionTimer (i.e. without suffix). drxShortCycleTimer Timerfor DRX in TS 36.321 [6]. Value in multiples of shortDRX-Cycle. A valueof 1 corresponds to shortDRX-Cycle, a value of 2 corresponds to 2 *shortDRX-Cycle and so on. extendedBSR-Sizes If value setup isconfigured, the BSR index indicates extended BSR size levels as definedin TS 36.321 [Table 6.1.3.1-2]. extendedPHR Indicates if power headroomshall be reported using the Extended Power Headroom Report MAC controlelement defined in TS 36.321 [6] (value setup). Otherwise the powerheadroom shall be reported using the Power Headroom Report MAC controlelement defined in TS 36.321 [6]. E-UTRAN always configures the valuesetup if more than one Serving Cell with uplink is configured. E-UTRANconfigures extendedPHR only if phr-Config is configured. The UE shallrelease extendedPHR if phr-Config is released. longDRX-CycleStartOffsetlongDRX-Cycle and drxStartOffset in TS 36.321 [6]. The value oflongDRX-Cycle is in number of sub-frames. Value sf10 corresponds to 10sub-frames, sf20 corresponds to 20 sub-frames and so on. IfshortDRX-Cycle is configured, the value of longDRX-Cycle shall be amultiple of the shortDRX-Cycle value. The value of drxStartOffset valueis in number of sub-frames. In case longDRX-CycleStartOffset-v1130 issignalled, the UE shall ignore longDRX-CycleStartOffset (i.e. withoutsuffix). maxHARQ-Tx Maximum number of transmissions for UL HARQ in TS36.321 [6]. onDurationTimer Timer for DRX in TS 36.321 [6]. Value innumber of PDCCH sub-frames. Value psf1 corresponds to 1 PDCCH sub-frame,psf2 corresponds to 2 PDCCH sub-frames and so on. periodicBSR-TimerTimer for BSR reporting in TS 36.321 [6]. Value in number of sub-frames.Value sf10 corresponds to 10 sub-frames, sf20 corresponds to 20sub-frames and so on. periodicPHR-Timer Timer for PHR reporting in TS36.321 [6]. Value in number of sub-frames. Value sf10 corresponds to 10subframes, sf20 corresponds to 20 subframes and so on. prohibitPHR-TimerTimer for PHR reporting in TS 36.321 [6]. Value in number of sub-frames.Value sf0 corresponds to 0 subframes, sf100 corresponds to 100 subframesand so on. retxBSR-Timer Timer for BSR reporting in TS 36.321 [6]. Valuein number of sub-frames. Value sf640 corresponds to 640 sub-frames,sf1280 corresponds to 1280 sub-frames and so on. sCellDeactivationTimerSCell deactivation timer in TS 36.321 [6]. Value in number of radioframes. Value rf4 corresponds to 4 radio frames, value rf8 correspondsto 8 radio frames and so on. E-UTRAN only configures the field if the UEis configured with one or more SCells. If the field is absent, the UEshall delete any existing value for this field and assume the value tobe set to infinity. The same value applies for each SCell (although theassociated functionality is performed independently for each SCell).shortDRX-Cycle Short DRX cycle in TS 36.321 [6]. Value in number ofsub-frames. Value sf2 corresponds to 2 sub-frames, sf5 corresponds to 5subframes and so on. In case shortDRX-Cycle-v1130 is signalled, the UEshall ignore shortDRX-Cycle (i.e. without suffix). sr-ProhibitTimerTimer for SR transmission on PUCCH in TS 36.321 [6]. Value in number ofSR period(s). Value 0 means no timer for SR transmission on PUCCH isconfigured. Value 1 corresponds to one SR period, Value 2 corresponds to2*SR periods and so on. SR period is defined in TS 36.213 [23, table10.1.5-1]. stag-Id Indicates the TAG of an SCell, see TS 36.321 [6]. Ifthe field is not configured for an SCell (e.g. absent inMAC-MainConfigSCell), the SCell is part of the PTAG. stag-ToAddModList,stag-ToReleaseList Used to configure one or more STAGs. E-UTRAN ensuresthat a STAG contains at least one SCell with configured uplink. If, dueto SCell release a reconfiguration would result in an ‘empty’ TAG,E-UTRAN includes release of the concerned TAG. timeAlignmentTimerSTAGIndicates the value of the time alignment timer for an STAG, see TS36.321 [6]. ttiBundling_UL TRUE indicates that TTI bundling TS 36.321[6] is enables while FALSE indicates that TTI bundling is disabled. TTIbundling can be enabled for FDD and for TDD only for configurations 0, 1and 6. For TDD, E-UTRAN does not simultaneously enable TTI bundling andsemi-persistent scheduling in this release of specification.Furthermore, E-UTRAN does not simultaneously configure TTI bundling andSCells with configured uplink. ttiBundling_DL TRUE indicates that TTIbundling TS 36.321 [6] is enabled for downlink while FALSE indicatesthat TTI bundling is disabled for downlink.

While the exemplary preceding ttiBundling_DL field represents onepossible Boolean ttiBundling_DL parameter, note that as anotherpossibility (among various other possibilities), such a parameter/fieldmight alternatively be described as follows (e.g., as a bitmapindicating DL TTI bundling status for each component carrier, or a 2-bitfield indicating DL TTI bundling status of the primary carrier with onebit and of all secondary carriers with one bit):

   ttiBundling_DL Each ‘1’ indicates that TTI bundling TS 36.321 [6] isenabled for downlink for a corresponding carrier, while each ‘0’indicates that TTI bundling is disabled for downlink for a correspondingcarrier.

Alternatively or additionally, a MAC-MainConfig IE that includes attiBundling_DL IE may be included within a RadioResourceConfigDedicatedIE, which is an IE that is used to setup/modify/release radio bearers,to modify the MAC main configuration, to modify a semi-persistentscheduling (SPS) configuration, and to modify a dedicated physicalconfiguration. In turn, the RadioResourceConfigDedicated IE may beincluded within an RRC message such as an RRCConnectionSetup message oran RRCConnectionReconfiguration message transmitted from the BS 102 tothe UE 106.

The indication to enable TTI bundling for downlink communications(whether communicated using an RRCConnectionSetup message,RRCConnectionReconfiguration message, and/or a MAC-MainConfig IE, and/orvia any other variation) may be provided for any of a variety ofreasons. In many cases, it may be determined to enable TTI bundling fordownlink communications if a downlink communication channel isexperiencing (or may be expected to experience) poor RF conditions. Forexample, if a UE 106 is near the edge of communicative range of the BS102, and/or if inherent propagation characteristics of a downlinkchannel result in greater signal attenuation, and/or if a downlinkcommunication channel is subject to maximum transmission powerlimitations, TTI bundling for communications via the downlinkcommunication channel might be implemented.

In 606, downlink communication may be performed between the BS 102 andthe UE 106 using TTI bundling. Depending on the TTI bundlingconfiguration (e.g., whether TTI bundling was indicated/enabled for onecomponent carrier or multiple/all component carriers in 604), thedownlink communication using TTI bundling may be performed on one ormore component carriers of the wireless communication link. For example,if TTI bundling is enabled on the secondary carrier but not the primarycarrier, downlink communications between the BS 102 and the UE 106 onthe secondary carrier may use TTI bundling, while downlinkcommunications between the BS 102 and the UE 106 on the primary carriermay not use TTI bundling.

Note that while typically for downlink data transfers (e.g., on thePDSCH in LTE), the BS 102 may specify transmission parameters (e.g.,MCS, Physical Resource Blocks assignment, HARQ process number, and theredundancy version (“rv”)), giving the BS 102 flexibility to choose alldownlink parameters every subframe, for downlink TTI bundling, it may bethe case that only one indication of downlink parameters may betransmitted (e.g., on the PDCCH in LTE) for each of the multiple“bundled” TTIs.

In such a case, the BS 102 may use any of a variety of options tospecify the downlink parameters for the multiple TTIs, and in particularfor the respective redundancy version of each TTI in a TTI bundle.

As a first possibility, the BS 102 may dynamically determine (and thusbe capable of changing at will) the redundancy version for each TTI whensending the downlink parameters.

As a second possibility, the BS 102 may initially select/determine theredundancy version order for TTI bundles, configure the selectedsettings using RRC signaling, then semi-statically use the configuredredundancy version order for subsequent TTI bundles without needing toexplicitly indicate as much with the downlink parameters for each TTIbundle.

As a third possibility, the BS 102 may be constrained by specificationconsiderations. For example, the redundancy version order for downlinkTTI bundles may be fixed in the 3GPP specification. In such a case, theBS 102 may utilize the fixed redundancy version order as specified whenperforming downlink communications using TTI bundling.

The second and third possibilities may reduce the number of bitscommunicated on the control channel (e.g., PDCCH) relative to the firstpossibility, but may reduce the flexibility of the BS 102 to select theredundancy version; accordingly, the selected option may depend on therelative priority and desirability of such considerations.

Note that at a subsequent time, if it is determined to disable downlinkTTI bundling on one or more carriers, one or more indications (e.g.,using the MAC-MainConfig RRC IE, or another suitable type of indication)to disable downlink TTI bundling on those carriers may be transmittedfrom the BS 102 to the UE 106, after which downlink TTI bundling may nolonger be performed on those carriers.

Thus, according to the scheme of FIG. 6, a wireless device may be ableto communicate with a cellular network using TTI bundling for downlinkcommunication.

FIG. 7—Downlink TTI Bundling Communication Scheme

FIG. 7 illustrates an exemplary downlink TTI bundling communicationscheme which may be used in conjunction with other aspects of thepresent disclosure. Note that FIG. 7 and the description thereof areprovided by way of example, and are not intended to be limiting to thedisclosure as a whole. Numerous alternatives to and variations of thedetails provided herein below are possible and should be consideredwithin the scope of the present disclosure.

The current concept of TTI bundling in 3GPP's LTE may include bundlingmultiple subframes into one uplink transmission by a UE to help a basestation (also referred to as an eNB or eNodeB in the LTE context) withreception for cell edge UEs (which may be power limited). By bundlingmultiple subframes together, the UE may be able to transmit more energyand more coded bits at one opportunity, thus creating a more robusttransmission.

TTI bundling has generally been used in the uplink only. Because themaximum transmission power of a UE (e.g., 23 dBm) may generally besignificantly less than that of a BS (e.g., 43 dBm), it has generallybeen considered unnecessary for base stations.

However, there may be circumstances in which downlink TTI bundling wouldbe beneficial. Certain of such circumstances may be illustrated by theexemplary possibility of using unlicensed ISM spectrum (e.g., 5.8 GHz)as a downlink communication channel.

As one example, if the downlink is at 5.8 GHz, and the uplink is at 2GHz, the propagation characteristics of DL will be different than UL.For example, in this exemplary scenario the downlink channel is likelyto be more strongly attenuated than the uplink channel. (or moregenerally, if the downlink is at a frequency subject tosignificant/strong attenuation). As another example, because of FCC(and/or other regulating bodies) requirements on the ISM band, which mayinclude (but are not necessarily limited to) reduced transmission power,the BS may have a transmission power constraint far lower than 43 dBm(e.g., 23 dBm).

Thus, in such a scenario, the DL may be “energy limited” and moreconstrained than the UL. In such a scenario, bundling subframes (TTIbundling) in the downlink may allow the BS to serve UEs with higherattenuation and increase the proportion of UEs that can be served by theISM band. More generally, providing the possibility to implement TTIbundling in the downlink may help balance UL and DL performance when ULand DL transmit powers are similar and UL frequencies have favorablepath-loss behavior (e.g., <2 GHz) and DL carrier frequencies have highpath-loss characteristics (e.g., 5.8 GHz).

As shown in FIG. 7, TTI bundling in the downlink may include bundlingdownlink subframes together in a single transmission instances (e.g.,using consecutive TTIs). By bundling downlink subframes together in asingle transmission (i.e., without waiting for an UL ACK/NACK) inchallenging channel conditions, the probability that the UE can decodeearly increases. This in turn has the potential to decrease latency.

If after a TTI bundled downlink transmission instance the UE has notsuccessfully extracted the data from the downlink transmission, it maystill be possible for the UE to provide a negative acknowledgement(“NACK”) to the BS to indicate as much. In this case (depending onsystem parameters, among other considerations), the BS may perform adownlink retransmission, which may include another TTI bundledtransmission instance.

Embodiments of the present disclosure may be realized in any of variousforms. For example some embodiments may be realized as acomputer-implemented method, a computer-readable memory medium, or acomputer system. Other embodiments may be realized using one or morecustom-designed hardware devices such as ASICs. Still other embodimentsmay be realized using one or more programmable hardware elements such asFPGAs.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of a methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

In some embodiments, a device (e.g., a UE 106) may be configured toinclude a processor (or a set of processors) and a memory medium, wherethe memory medium stores program instructions, where the processor isconfigured to read and execute the program instructions from the memorymedium, where the program instructions are executable to implement anyof the various method embodiments described herein (or, any combinationof the method embodiments described herein, or, any subset of any of themethod embodiments described herein, or, any combination of suchsubsets). The device may be realized in any of various forms.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. A base station (BS), comprising: a radio; and a processing element operably coupled to the radio; wherein the radio and the processing element are configured to: establish a wireless communication link with a wireless user equipment device (UE) according to a first radio access technology (RAT); configure transmission time interval (TTI) bundling for downlink communications with the UE using the first RAT; and perform downlink communications with the UE using the first RAT using TTI bundling after providing the configuration, wherein said performing comprises, for each TTI bundle, transmitting a control channel message indicating downlink parameters for each respective TTI bundle, wherein the downlink parameters comprise a redundancy version (RV), and wherein the RV for each TTI of each respective TTI bundle is determinable based on the downlink parameters.
 2. The BS of claim 1, wherein each TTI bundle comprises multiple downlink subframes having different HARQ redundancy versions in a transmission instance using multiple consecutive TTIs.
 3. The BS of claim 1, wherein the radio and the processing element are further configured to: receive a negative acknowledgement from the UE for a TTI bundle transmitted; and provide a retransmission TTI bundle to the UE.
 4. The BS of claim 1, wherein the radio and the processing element are further configured to: configure TTI bundling based on one or more of: maximum downlink transmit power limitations; propagation characteristics of a frequency channel used by the wireless communication link; and current channel conditions.
 5. The BS of claim 1, wherein TTI bundling for downlink communications with the UE is configured based at least in part on the wireless communication link being established on a frequency channel in an unlicensed frequency band.
 6. The BS of claim 1, wherein the control channel message additionally indicates a redundancy version (RV) order for the TTI bundle and for subsequent TTI bundles.
 7. The BS of claim 1, wherein the radio and the processing element are further configured to: provide an indication to the UE to disable TTI bundling for downlink communications with the UE; and perform downlink communications with the UE without using TTI bundling after providing the indication.
 8. A base station (BS), comprising: a radio; and a processing element operably coupled to the radio; wherein the radio and the processing element are configured to: establish a wireless communication link with a first user equipment device (UE) according to a first radio access technology (RAT); establish a wireless communication link with a second UE according to the first radio access technology (RAT); configure, via a first indication, transmission time interval (TTI) bundling for downlink communications with the first UE using the first RAT, wherein TTI bundling comprises bundling multiple downlink subframes into at least one TTI bundle; configure, via a second indication, transmission time interval (TTI) bundling for downlink communications with the second UE using the first RAT; perform downlink communications with the first UE using the first RAT using TTI bundling after providing the first indication, wherein said performing comprises, for each TTI bundle: transmitting a first control channel message indicating downlink parameters for each respective TTI bundle, wherein the downlink parameters comprise a redundancy version (RV); and perform downlink communications with the second UE using the first RAT using TTI bundling after providing the second indication, wherein said performing comprises, for each TTI bundle: transmitting a second control channel message that does not indicate the redundancy version in order to reduce the number of bits in the control channel, wherein an order of RVs for respective TTIs of each TTI bundle is determined from a fixed configuration.
 9. The BS of claim 8, wherein the first control channel message additionally indicates a RV order for subsequent TTI bundles.
 10. The BS of claim 8, wherein each TTI bundle comprises multiple downlink subframes having different HARQ redundancy versions in a transmission instance using multiple consecutive TTIs.
 11. The BS of claim 8, wherein the radio and the processing element are further configured to: receive a negative acknowledgement from the first UE for a TTI bundle transmitted; and provide a retransmission TTI bundle to the first UE.
 12. The BS of claim 8, wherein the radio and the processing element are further configured to: configure TTI bundling based on one or more of: maximum downlink transmit power limitations; propagation characteristics of a frequency channel used by the wireless communication link; and current channel conditions.
 13. The BS of claim 8, wherein TTI bundling for downlink communications with the first UE is configured based at least in part on the wireless communication link being established on a frequency channel in an unlicensed frequency band.
 14. The BS of claim 8, wherein the indication comprises a parameter of an RRC or MAC configuration message transmitted to the UE via a control channel.
 15. A user equipment device (UE), comprising: a radio; and a processing element operably coupled to the radio; wherein the radio and the processing element are configured to: establish a wireless communication link with a base station (BS) according to a first radio access technology (RAT); receive a configuration of transmission time interval (TTI) bundling for downlink communications using the first RAT; perform downlink communications with the BS using the first RAT using TTI bundling after receiving the configuration, wherein said performing comprises, for each TTI bundle, receiving a control channel message indicating downlink parameters for each respective TTI bundle, wherein each TTI bundle is processed according to a redundancy version (RV) comprised within the respective downlink parameters.
 16. The UE of claim 15, wherein each TTI bundle comprises multiple downlink subframes having different HARQ redundancy versions in a transmission instance using multiple consecutive TTIs.
 17. The UE of claim 15, wherein the radio and the processing element are further configured to: transmit a negative acknowledgement to the BS for a TTI bundle received; and receive a retransmission TTI bundle from the BS.
 18. The UE of claim 15, wherein TTI bundling for downlink communications with the BS is configured based at least in part on the wireless communication link being established on a frequency channel in an unlicensed frequency band.
 19. The UE of claim 15, wherein the control channel message additionally indicates a redundancy version (RV) order for the TTI bundle and for subsequent TTI bundles.
 20. The UE of claim 15, wherein the radio and the processing element are further configured to: receive an indication from the BS to disable TTI bundling for downlink communications with the BS; and receive downlink communications from the BS without using TTI bundling after receiving the indication. 